A method for forming a ferrite coating on a substrate has been known, for example, as disclosed in Japanese Provisional Patent Publication No. 65085/1988 in which an oxidizer solution and a ferrous ion solution are added to a deoxidized solution containing particulate and/or fibrous substrates to form a thin ferrite coating on the particulate and/or fibrous substrates. However, according to this method, by-products are liable to be formed and a stable and controlled magnetic film could be obtained with difficulty.